Systemic sclerosis (SSc) is a multi-system, fibrotic disease that affects the skin and a variety of internal organs. Persistent myofibroblast activation and associated excessive extracellular matrix protein (ECMs) deposition are hallmarks of the disease. The mechanisms that account for this excessive fibrotic response remain elusive. Despite its high mortality and morbidity, there are no FDA approved medications for fibrotic complications of SSc. Our recent work indicates that a RNA-processing mechanism known as alternative polyadenylation (APA) is critical for the upregulation of profibrotic genes in dermal fibrosis through 3? UTR tail shortening of key transcripts. Recent evidence demonstrated that a key regulator of APA is Cleavage factor Im 25 (CFIm25). The CFIm25 deletion leads to 3? UTR shortening. A truncated 3? UTR tail will often lack microRNA binding sites and evades the microRNA-mediated gene repression. Our preliminary data indicate CFlm25 is downregulated in fibrotic skin of SSc patients and in murine dermal fibrosis models. Knockdown of CFIm25 in normal skin fibroblasts is sufficient to promote the 3? UTR shortening of key profibrotic genes. Moreover, the central fibrotic cytokine TGF? suppresses CFIm25 expression through miR-203 upregulation. Overall, our data uncovered a novel mechanism by which TGF? mediated CFIm25 downregulation leads to 3? UTR shortening and the over-production of profibrotic factors and ECMs, and contributes to the pathogenesis of SSc. Based on this preliminary data, the main hypothesis of this project is that TGF? and miR-203 downregulate CFIm25 in fibroblasts, resulting in dermal fibrosis by upregulation of profibrotic genes and ECMs through 3? UTR shortening. This hypothesis will be examined in the following specific aims: Aim I: Define the fibroblast specific contribution of CFIm25 depletion in dermal fibrosis murine models. This aim will elucidate the downstream effects of CFIm25 depletion on key fibrotic pathways. Aim II: Determine the mechanisms for CFIm25 downregulation and assess their potential as therapeutic targets in dermal fibrosis. The mechanisms for TGF? mediated miR-203 downregulation and subsequent CFIm25 repression by miR-203 will be elucidated. This aim will characterize the upstream events leading to CFIm25 depletion and will identify potential therapeutic targets. Aim III: Characterize CFIm25 in SSc human skin/fibroblasts and identify fibrotic genes dysregulated by APA. Serial dermal fibroblasts and skin samples from patients with early SSc and matched controls will be examined using a novel RNA sequencing technology. This aim will provide for the first time an unbiased, longitudinal view of CFIm25 mediated APA profile in a fibrotic disease. The proposed research links for the first time the CFIm25 mediated 3? UTR shortening to dermal fibrosis. This can lead to discovering a key mechanism that amplifies the fibrotic response in SSc and ultimately to identifying an entirely novel target for treatment of persons with this potentially devastating disease.